Heat pumps are a particularly elegant and energy saving installation for low temperature and warm water providing units. They are capable of pumping heat from a low temperature level, e.g. well water of 10° C. for example, up to a temperature of 30-50° C. According to the parameters of such a unit, performance numbers of up to 6 may be achieved. (The performance number indicates how much the heat power of the unit is greater in comparison to the electrical power supplied). Efficient so-called water/water-heat pumps, however, can involve the supply of not inconsiderable quantities of water obtained from wells. The water, that has been cooled in the heat pump, has subsequently to be fed to the groundwater via absorption wells. This will, in general, not only result in extremely high investments, but is refused to an increasing extent by the authorities in view of the risk of a groundwater pollution.
Another method is to withdraw heat from ambient air. Such installations involve a very high throughput of air, which can lead to rather modest performance numbers and to emission of noise. Typically, icing of the heat exchangers will occur in winter time which requires regular defrosting and which further reduces the average performance number.
In order to solve the problems of high water consumption in water/water installations and, at the same time, to improve the performance number, a variant to the known systems has been suggested in DE 101 39 065 A1. According to this publication, a solar collector mounted on a roof is provided which is connected to a water reservoir, the heated water of which is heating the evaporator of a heat pump, while the latter pumps the heat supplied onto a higher temperature level.
Devices of this kind have, in practice, shown not to be without problems:
Although some improvement was possible by this solution, the environmental problem is still present, though with a different argumentation: to avoid icing of the system, particularly of the solar collector in winter time, the water in this circuit is provided with an anti-freezer, e.g. glycol or with sodium chloride. In case there is some leakage in the system, a relative large quantity of water contaminated with the anti-freezer can emerge and may finally reach the groundwater.
This is the reason why the authorities refuse to an increasing extent to approve such installations, not only in preservation regions of groundwater, but also in many other regions of an ambient worthwhile to be protected.
A further reason, which can deter home-owners and potential installers from such installations, is, on the one hand, the unfavorable appearance: the absorbers, consisting either of glass enclosed boxes which surround the proper collectors, or of a black plastic material, are mounted on the roofing and contrast, in general, very much to the roofing that consists of roofing stones or tiles, or of color coated aluminum plates so that the appearance of a house having such an installation is much affected from an aesthetic point of view. In view of the relative high prize of such collectors, but also for aesthetic reasons, one therefore tries to do with a minimum collector surface, which, however, results in a low performance number of the heat pump over the annual average.
It has also been suggested to utilize the temperature rise of roofs by irrigating it with water and to introduce the water, thus heated, into a cistern. Cistern water is fed by a pump through a heat exchanger to the distributing pipes on the roof's surfaces. Such installations are described, for example, in the German Patent Application DE 33 10 228 and in the French Patent Application FR 2 566 032. Similar installations are subject matter of the U.S. Pat. No. 4,340,036, the U.S. Pat. No. 4,052,975 and the U.S. Pat. No. 2,660,863. Installations of this type work as long as the cistern water has a temperature clearly above 0° C. However, problems can appear when the temperature of the cistern water drops down to the range of 0° C. For example, weather conditions can occur in the months of January and February in many regions of Central Europe where, due to fog, a temperature rise of the roof's surface by direct and, to a wide extent also by indirect, radiation fails to appear, while the air temperature is below 0° C. With such weather conditions, the need of heat can be great, but cannot be covered, or only be partially covered, by the above-mentioned installations so that one has to fall back to an additional heating which is, in general, an electrical heating. Then, the performance number of the installation is in the range of 1 and leads to worsening of the annual performance number that can be decisive for judging the efficiency of the heating installation.
In the arrangement of the heat exchanger, as is illustrated, for example, in DE 33 10 228, such temperatures result in icing of the heat exchanger, beginning at the feeding conduit for the brine which has been cooled down in the heat pump to, for example, −4° C. Such icing can be unavoidable when utilizing the latent heat of the water, but the formation of large and massive volumes of ice can be avoided.
The contents of all documents mentioned herein, and throughout the application, are incorporated herein by reference in their entireties.